From Coinage Metal to Luminescent Nanodots: The Impact of Size on Silver's Optical Properties

摘要

Nanoscience has become a topic covered in undergraduate education. The new properties gained as matter becomes nanoscale are especially useful to illustrate the impact of size. Silver is a good example for such an illustration because it displays completely different properties at different sizes, such as bulk silver, nanoparticles, and few-atom nanodots. Such differences reflect the interaction between photons and the varied silver species. A simple demonstration was designed to illustrate the property change as the silver diminished from bulk phase to silver nanodots. Without any protection, silver ions are reduced directly to large silver particles. The introduction of a protection group, such as poly(acrylic acid), facilitates the formation of silver nanoparticles, which shows strong visible absorption due to surface plasmon resonance. However, subtle adjustment of the protection group by amino-functionalized alkylsilane is required to obtain stable silver nanodots that display not only strong absorption but also bright emission. This demonstration is a general tutorial for upper-level undergraduate students who have an introductory background of photophysics.